1. Field of the Invention
The present invention relates to an image display device, or more particularly, to an image display device for switching the direction of polarization in which light coming from a display element is polarized so as to increase the number of apparent pixels.
2. Description of the Related Art
In the past, various proposals have been made for an image display device for switching the direction of deflection, in which light coming from a display element is polarized, so as to increase the number of apparent pixels. For example, Japan Unexamined Patent Publication No. 6-324320 describes an image display device to be used with an optical member, which varies an optical path for each field, interposed between the image display device and an observer or screen. A pattern of pixels whose displayed positions are duplicated according to a magnitude by which the optical path is varied for each field is displayed on the image display device.
The image display device is made by arranging an LCD, a polarization switching liquid crystal cell (a plane-of-polarization rotation plate), a birefringent plate, and an eyepiece in that order. The LCD serves as an image display unit. The polarization switching liquid crystal cell, serving as an optical member, has a plurality of electrodes. The birefringent plate refracts light according to the direction of polarization. The eyepiece magnifies an image. The polarization switching liquid crystal cell is used to control the direction of polarization according to the timing of scanning the LCD. The pixels constituting an image to be displayed on the LCD are thus duplicated.
The direction of polarization is controlled according to the timing of scanning the LCD. This is, as described in the above patent publication, because pixels written in an LCD persist over the next field, and information of an odd field and information of an even field therefore coexist in one screen.
Japanese Unexamined Patent Publication No. 9-325204 describes a technology for improving the transmittance of a birefringent plate used as an optical filter. Specifically, the birefringent plate is made from lithium niobate that exhibits a high double refractive index, and is designed thinly. Moreover, the surface of the birefringent plate is coated with an anti-reflective (AR) coating in order to suppress surface reflectance that is more serious than that occurring on a crystal or the like.
Moreover, Japanese Unexamined Patent Publication No. 9-281430 describes a technology according to which a prism realizing an eccentric optical system, being symmetric with respect to a plane, and having a free-form surface is used as an image magnification eyepiece.
However, according to the arrangement described in the Japanese Unexamined Patent Publication No. 6-324320, as described later in conjunction with FIG. 4A, FIG. 4B, and FIG. 5, gaps among the electrodes included in the polarization switching liquid crystal cell are observed as streaks which eventually impair image quality. This has been demonstrated experimentally by the present applicant.
Moreover, when polarized light obliquely enters the birefringent plate, flickers are observed as described later in conjunction with FIG. 10A, FIG. 10B, and FIG. 11. Namely, since the transmittance of the birefringent plate for light varies depending on the relationship between the direction of polarization for the light and the direction of incidence thereof, an amount of transmitted light varies with every switching of the direction of polarization by the polarization switching liquid crystal cell. This has been demonstrated experimentally by the present applicant.
Furthermore, the optical filter described in the Japanese Unexamined Patent Publication No. 9-325204 is used to improve a transmittance for light but is not intended to control the direction of polarization. No mention is made of a means for alleviating occurrence of the foregoing flickers.
There is a demand for an image display device having the structure including the optical system described in Japanese Unexamined Patent Publication No. 9-281430, but without the foregoing drawbacks and enabling saving space.
One object of the present invention is to provide an image display device capable of displaying an easy-to-see image while making unnecessary streaks or the like indiscernible.
Another object of the present invention is to provide an image display device capable of displaying an easy-to-see image by minimizing occurrence of flickers or the like.
Briefly, according to the present invention, there is provided an image display device including a display element, a polarization control means, an optical path control means, and an optical system. The display element has a plurality of pixel locations arrayed regularly. The polarization control means controls a plurality of electrodes incorporated therein so as to switch the direction of polarization, in which incident light coming from the display element is polarized, in units of a portion composed of electrodes, and then emits resultant light. The optical path control means lies on the optical path of the light emitted from the polarization control means, and varies the optical path according to the direction of polarization. The optical system magnifies light having passed through the optical path control means and representing an image displayed by the display element. The display element and polarization control means are positioned so that: the position of a virtual image stemming from the display element due to the optical system and the position of a virtual image stemming from the electrodes included in the polarization control means will be separated from each other by a distance equal to or longer than a depth of field.
Moreover, according to the present invention, there is provided an image display device including a display element, a polarization control means, an optical path control means, and an optical system. The display element has a plurality of pixel locations arrayed regularly. The polarization control means controls a plurality of electrodes incorporated therein so as to switch the direction of polarization, in which incident light coming from the display element is polarized, in units of a portion composed of electrodes. The optical path control means lies on the optical path of light emitted from the polarization control means, and varies the optical path depending on the direction of polarization. The optical system magnifies light having passed through the optical path control means and representing an image displayed on the display element. The polarization control means is positioned so that the position of a virtual image stemming from the electrodes in the polarization control means will be a closer range than a near point adjustment limit or the shortest distance at which the human eyes can come into focus.
Furthermore, according to the present invention, there is provided an image display device including a display element, a polarization control means, an optical path control means, and an eccentric optical system. The display element has a plurality of pixel locations arrayed regularly. The polarization control means controls a plurality of electrodes incorporated therein so as to switch the direction of polarization, in which incident light coming from the display element is polarized, in units of a portion composed of electrodes. The optical path control means lies on the optical path of light emitted from the polarization control means, and varies the optical path depending on the direction of polarization. The eccentric optical system magnifies light having passed through the optical path control means and representing an image displayed on the display device. The polarization control means is tilted relative to the display element.
According to the present invention, there is provided an image display device including a display element, a polarization switching means, a birefringent optical element, and an optical system. The display element has a plurality of pixel locations arrayed regularly. The polarization switching means switches the direction of polarization, in which incident light coming from the display element is polarized, to two substantially orthogonal directions, and emits resultant light. The birefringent optical element lies on the optical path of light emitted from the polarization switching means, and varies the optical path depending on the direction of polarization. The optical system magnifies light having passed through the birefringent optical element and representing an image displayed on the display element. At least part of the surface of the birefringent optical element is finished so that the ratio of transmittances of polarized light, which is emitted from the polarization switching means and travelling in the two substantially orthogonal directions, will be approximated to 1.
In addition, according to the present invention, there is provided an image display device including a display element, a polarization switching means, a birefringent optical element, and an optical system. The display element has a plurality of pixel locations arrayed regularly. The polarization switching means switches the direction of polarization, in which incident light coming from the display element is polarized, to two substantially orthogonal directions. The birefringent optical element lies on the optical path of light emitted from the polarization switching means and varies the optical path depending on the direction of polarization. The optical system magnifies light having passed through the birefringent optical element and representing an image displayed on the display element. At least part of the surface of the optical system is finished so that the ratio of transmittances of polarized light, which is emitted from the polarization switching means and travelling in the two substantially orthogonal directions, will be approximated to 1.
These objects and advantages of the present invention will become further apparent from the following detailed explanation.